Bikkurim, Chapter Two, Mishnah Nine
This mishnah notes ways in which a koy is similar to a hayyah, a wild animal (see previous mishnah).
How is it like a wild animal?
1) Its blood must be covered like the blood of a wild animal.
2) It may not be slaughtered on a festival.
3) If he slaughtered it, he should not cover its blood.
4) Its fat is impure like that of a wild animal, but its impurity is of doubtful status.
5) One does not redeem with it the first-born of a donkey.
Section one: When one slaughters a hayyah one must pour the blood out on the ground and cover it (Leviticus 17:13). Since a koy might be a hayyah, one should do the same with a koy.
Section two: Preparation of food, including slaughtering, is permitted on Yom Tov, the first and last days of Pesah and Sukkot, and Shavuot. The problem with slaughtering a hayyah is that it is prohibited to dig up dirt in order to cover its blood. If there is already dirt set aside for this use, then one can slaughter a hayyah. However, when it comes to a koy, there is another problem–one cannot use even dirt that has already been dug up, because if the koy is actually a domesticated beast, then the dirt is muktzeh because it could not have been set aside to cover blood. Therefore, one cannot slaughter a koy on Yom Tov.
Section three: If he nevertheless did slaughter a koy, he should not cover its blood. It might not be a hayyah, in which case covering its blood would not be necessary.
Section four: A certain type of fat, called helev, is impure when it comes from a hayyah but not when it comes from an improperly slaughtered behemah. When it comes to the koy, we must be concerned lest it really is a hayyah, and therefore we need to treat its fat as if it was impure. However, the status of the impurity that it conveys is only doubtful because it may indeed be a behemah. This has certain ramifications that I do not wish to get into here.
Section five: A first-born donkey must be redeemed by giving the priest a first born sheep in its stead (Exodus 13:13). Although a koy might be related to a sheep, or perhaps be a type of sheep, it cant be used to redeem a first born donkey, because it might be a wild animal.